Psychopharmacology of male rat sexual behavior: modeling human sexual dysfunctions?

Chronic levamisole exposure in male rats alters sexual behavior and induces apoptosis in the testis

Levamisole is an anti-helminthic drug developed and introduced in veterinary medicine, and it has been used more frequently after the inclusion of its usage in human medicine regarding disorders with immunomodulatory properties. In recent years, it has started to attract attention since it has beneficial effects on the treatment of COVID-19 due to its immunomodulatory properties. To investigate the effects of levamisole on sexual behavior and the reproductive system in male rats, two groups were formed the vehicle (n = 10) and levamisole (n = 10) groups. The vehicle group was given purified water whereas the levamisole group was administered with levamisole (2 mg/kg) by oral gavage daily for 4 weeks. Levamisole treatment significantly increased the mount latency (ML, P < 0.001) as well as the intromission latency (IL, P < 0.01). It also significantly prolonged postejaculatory interval (PEI, P < 0.01), decreased copulatory rate (CR, P < 0.05), and sexual activity index (SAI, P < 0.05). It significantly decreased serum monoamine oxidase A (MAO-A) levels (P < 0.05). Additionally, levamisole induced disorganizations of germinal epithelial cells of seminiferous tubules, congestion, edema in the interstitial area, and metaphase arrest in some spermatocytes (P < 0.001), and it significantly increased the immunohistochemical expressions of apoptotic Bax and cytochrome c, which is crucial proapoptotic protein, in the testis (P < 0.001). Also, levamisole significantly upregulated the mRNA levels of the apoptosis-related key regulatory genes, including Bax (Bcl-2-associated X protein, P = 0.05) and Bax/Bcl-2 ratio (P < 0.01) in testis. The current research is the first to show that levamisole may decrease sexual performance, potency, sexual motivation, and libido and induce apoptosis in the testis.

Withania somnifera ameliorates sexual arousal and impotence in stressed sexually sluggish male rats by modulating neurotransmitters and NO/cGMP/PDE5α pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Psychological stress is a growing global threat to male sexual potency and erection efficiency. Withania somnifera (L.) Dunal (WS), also known as Ashwagandha, is a well-known Ayurvedic herb. The roots of Withania somnifera improve the body's ability to handle stress, strengthen the immune system, promote healthy ageing, and have aphrodisiac properties with male sexual stimulation effects. Despite its widespread acceptance as an Ayurvedic stress-relieving drug with beneficial effects on male reproductive health, Withania somnifera has yet to be studied for its potential role in improving the sexual arousal and erectile dysfunction of psychologically stressed sexually sluggish males.

AIM OF THE STUDY

To investigate the therapeutic effects of purified root powder of Withania somnifera on sexual behaviour and erectile efficiency in stressed sexually sluggish male rats.

MATERIALS AND METHODS

Sexually sluggish male rats were screened by premating tests after being exposed to a psychological stressor, restraint stress, 3 h/day for 30 days. Subsequently, these rats were treated with purified root powder of WS (150 or 300 mg/kg/day-PO) or sildenafil (5 mg/kg/day-PO) for 30 days. The rats were sacrificed after 24 h of the last treatment, and the effects on various factors related to sexual behaviour, penile histomorphology, serum hormones, and neurotransmitters associated with sexual arousal and penile erection were examined.

RESULTS

WS treatment improves prosexual and sexual behaviour in psychologically stressed sexually sluggish male rats by increasing non-contact erections and mounts, intromission, and ejaculation frequencies, while decreasing sexual exhaustion by decreasing post-ejaculation intervals and latencies. WS also modulates neurotransmitters and hormones associated with sexual desire and stress, including dopamine, serotonin, corticosterone, and prolactin. Additionally, there was also a dose-dependent increase in serum LH, FSH, and testosterone levels. The administration of WS to sexually sluggish rats resulted in significant improvements in penile histomorphology, specifically by increasing the ratio of smooth muscle (SM) to collagen. Furthermore, in sexually sluggish rats, WS treatment increased the expression of markers associated with penile erection facilitation, such as nNOS, eNOS, p-Akt, nitric oxide, acetylcholine, and cGMP. Notably, WS treatment decreased the expression of penile PDE5α in these rats in a dose-dependent manner. Remarkably, the therapeutic effects of WS are comparable to those of sildenafil.

CONCLUSIONS

Purified root powder of Withania somnifera was found to improve sexual arousal and erection efficiency in stressed, sexually sluggish male rats. This improvement was achieved by modulating the HPG and HPA axes as well as the NO/cGMP/PDE5α pathway involved in penile erection. Thus, our findings strongly support the potent therapeutic potential of purified root powder of WS in improving the sexual health of stressed sexually sluggish rats.

A new approach to 'on-demand' treatment of lifelong premature ejaculation by treatment with a combination of a 5-HT1A receptor antagonist and SSRI in rats

Lifelong premature ejaculation (PE) in men lacks an adequate on-demand pharmacological treatment. Although selective serotonin reuptake inhibitors (SSRIs) are used for PE they only work after chronic treatment, or if used on-demand, less adequately than chronic SSRI treatment. It has been shown that the addition of a behaviorally silent 5-HT1A-receptor antagonist to an SSRI can generate acute inhibitory effects on male rat sexual behavior. Atlas987 is a selective 5-HT1A-receptor antagonist with equal potency to displace agonist and antagonist binding to pre- and post-synaptic 5-HT1A receptors in rat and human brain. To investigate whether Atlas987 together with the SSRI paroxetine, a combination called Enduro, induces acute inhibitory effects on male rat sexual behavior, we tested Enduro in Wistar rats in a dose-dependent manner. We first tested the 5-HT1A receptor antagonist Atlas987 in 8-OH-DPAT induced serotonergic behavior in rats. Second, we tested Enduro in a dose-dependent manner in male sexual behavior. Third, we tested the effective time window of Enduro's action, and lastly, we measured the plasma levels of Atlas987 and paroxetine over an 8-h period. Results showed that Enduro acutely and dose-dependently reduced the number of ejaculations and increased the ejaculation latencies. The behavioral pattern induced reflected a specific effect on sexual behavior excluding non-specific effects like sedation or sensoric-motoric disturbances. The time-window of activity of Enduro showed that this sexual inhibitory activity was at least found in a 1-4 h' time window after administration. Plasma levels showed that in this time frame both Atlas987 and paroxetine are present. In conclusion, in rats, Enduro is successful in acutely inhibiting sexual behavior. These results may be therapeutically attractive as "on demand" treatment for life-long premature ejaculation in men.

Effects of tadalafil on sexual behavior of male rats induced by chronic unpredictable mild stress

Background

Few studies have investigated psychogenic sexual dysfunction including psychogenic erectile dysfunction (pED); the effect of tadalafil on sexual behavior of male rats induced by chronic unpredictable mild stress (CUMS) remains unclear.

Aim

The aim was to explore the influence of CUMS on sexual behavior of male rats and the effects of tadalafil on that.

Methods

Adult male rats were divided into 3 groups, including the normal group without CUMS, the model group with 6 weeks' CUMS, and the tadalafil group with treatment of tadalafil during CUMS. CUMS consists of water deprivation, food deprivation, stroboscopic lightning, white noise, cage tilting, weeding packing, and housing 2 unfamiliar rats. The apomorphine test and vaginal smear test were conducted with the aim to screen out male rats with good erectile function and make preparation for the sexual behavior test, respectively.

Outcomes

At the end of the study period, the level of anhedonia and sexual function were evaluated by the sucrose preference test, sexual behavior test, and measurement of serum testosterone, dopamine, and 5-HT.

Results

Sucrose preference showed significant decrease in rats after CUMS. The intromission ratio and total intromission frequency decreased significantly, while the mount latency and ejaculation latency prolonged significantly in CUMS-induced rats when compared with normal rats. Meanwhile, the treatment of tadalafil reversed the level of anhedonia and sexual function in CUMS-induced rats. However, there were no statistical differences in the levels of serum testosterone, dopamine, and 5-HT among groups.

Clinical Implications

The study constructed an animal model that can provide clinical insights into the mechanism of psychogenic sexual dysfunction and supports the application of tadalafil in pED therapy.

Strengths and Limitations

We found that CUMS-induced rats exhibited anhedonia and poor sexual function that could be prevented by tadalafil administration. Future research needs to construct the standard of pED model and explore the mechanism of tadalafil on central nervous system.

Conclusion

Tadalafil could prevent the changes of depression and poor sexual function in rats induced by CUMS, and the method of CUMS and the sexual behavior test should be used in the future for pED modeling.

Effects of One-Shot Hyaluronic Acid Injection in Lifelong Premature Ejaculation: A Pilot Study

The therapeutic management of premature lifelong ejaculation (PE) ranges from behavioral therapy to pharmacological and surgical treatments. Hyaluronic Acid (HA) injection into the glans penis is a non-surgical procedure, intended to reduce glans hypersensitivity, improving the intravaginal ejaculation latency time (IELT). HA injection can be performed through different techniques that, although safe and effective, rarely can cause local complications. In this pilot uncontrolled study, we tested the effectiveness of a new technique based on a single HA injection into the frenulum of the glans, to improve IELT in a sample of patients affected by PE. We observed a significant increase of the IELT after one (median 73.3, IQR 66.2–79.9 s) and two months (66.2, 63.1–73.9) that gradually decreased at three months, remaining still significantly higher than at baseline (34.8, 30.9–37.4). PEDT and IIEF questionnaires significantly improved compared to baseline in the first two months of follow-up (p < 0.001). In conclusion, the preliminary results emerging from this pilot uncontrolled study, highlight the effectiveness of this one-shot HA injection approach, although a larger sample and longer follow-up time are needed to standardize the procedure.

A Protocol for the Non-invasive Method of Ultrasound Separation During the Sociosexual Vocal-Non-contact Model in Rats

Ultrasonic vocalization (USV) is one of the measurable behavioral parameters of sociosexual interactions in rats. To precisely and accurately describe the neurobehavioral properties of USV and the potentially related specific emotional responsiveness of animals, we need to know which animals vocalize and what is their exact behavioral and physiological response. To this end, we modified the non-contact cage [non-contact erection model (NCE)] by adding a modification [vocalization-non-contact erection (VOC-NCE)] that makes it possible to assign emitted ultrasonic signals to a particular animal. Typically, the NCE cage consists of two compartments separated by perforated baffles. A male is placed in one section, and a receptive female is placed in the other section. This makes possible the accurate description of sexual parameters related to the cues controlled by the experimenter. In VOC-NCE, we completely separated the male USV from the female USV by three appropriately perforated baffles and located microphones combined with ultrasonic screening. We recorded emission in both typical bands, the so-called 22- and 50-kHz bands, with various subtypes, thus highlighting the utility of our protocol to investigate the sexual dimorphism of vocalization. Similar to the anticipatory model, we showed that emission can occur without acoustic feedback from concomitants during the VOC-NCE test. Therefore, we propose a relatively simple method for assigning individual vocalization. We discuss its usefulness and limitations in assessing vocal differentiation related to sexual parameters, adaptive changes during conditioning procedures, and further applications.

Irisin ameliorates male sexual dysfunction in paroxetine-treated male rats

Sexual dysfunction is a common clinical condition due to different causes including the use of selective serotonin reuptake inhibitors (SSRI). Especially, SSRI paroxetine is known to cause numerous types of sexual dysfunction in men. There is growing interest in exercise as a non-pharmacological approach for the treatment of SSRI-induced sexual dysfunction. With these in mind, we investigated the effects of irisin, which is a recently detected exercise-linked hormone, on paroxetine-induced sexual dysfunction in male rats. Our findings showed that circulating irisin levels were lower in paroxetine-induced sexual dysfunction in male rats (20 mg/kg/day for 8 weeks by oral gavage than in vehicle-treated rats). In addition, results from sexual behavioral tests revealed that subcutaneous irisin perfusion (100 ng/kg/day via mini-osmotic pumps for 28 days) ameliorated sexual motivation and copulatory performance in sexually impaired male rats treated with paroxetine. The significantly reduced serum testosterone levels and α1-adrenoceptors (ADRA1A) and tyrosine hydroxylase gene (TH) expression levels in the nucleus accumbens (NAc) in paroxetine-induced sexually dysfunctioning male rats were markedly increased following irisin exposure. Similarly, the expression levels of ADRA1A and TH in the medial preoptic area (mPOA) significantly increased in male rats co-administered with paroxetine and irisin compared to the vehicle-treated male rats. These results demonstrate that irisin may be a therapeutic modality that mimics/supports the beneficial effects of exercise for improving SSRI-associated sexual dysfunction in men through increase in serum testosterone levels and increased expression of α1-adrenoceptors and TH in the NAc and mPOA associated with sexual motivation and copulatory behaviors.

An update on the treatment of premature ejaculation: A systematic review

To analyse the current therapeutic options for patients with premature ejaculation (PE) and highlight their mechanism(s) of action, effectiveness, advantages and limitations. A literature search was conducted using the PubMed database searching for articles exploring different PE treatment modalities. A Preferred Reporting Items for Systemic Reviews and Meta-Analyses (PRISMA) approach was used to report the results of the literature search. A total of 149 articles were included in this review. The currently available treatment methods for PE include behavioural therapy, local anaesthetics, tricyclic antidepressants, selective serotonin reuptake inhibitors, and selective phosphodiesterase inhibitors. Most PE treatments are either experimental or used off-label. New treatments are certainly warranted to overcome this exasperating sexual dysfunction.

Abbreviations: AIPE: Arabic Index of Premature Ejaculation; CNS: central nervous system; CYP: cytochrome P450; ED: erectile dysfunction; FDA: United States Food and Drug Administration; H1: histamine receptors; 5-HT: 5-hydroxytryptamine; IELT: The intravaginal ejaculation latency time; IPE: Index of Premature Ejaculation; M1: muscarinic receptors; OCD: obsessive–compulsive disorder; PDE5: phosphodiesterase type 5; PE: premature ejaculation; PEP: Premature Ejaculation Profile; PRO: patient-reported outcome; RCT: randomised controlled trial; SS: Severance Secret (cream); SSRIs: selective serotonin reuptake inhibitors; TCAs: tricyclic antidepressants

Expression of brain-derived neurotrophic factor in rapid ejaculator rats: A further study

Limited evidence has indicated that brain-derived neurotrophic factor (BDNF) may be involved in the neurobiology of premature ejaculation (PE). This study aimed to investigate BDNF levels in the central and peripheral nervous systems of a rapid ejaculation model. Eighteen male rats were selected and classified as 'sluggish', 'normal' and 'rapid' ejaculators on the basis of ejaculation frequency during copulatory behavioural tests. BDNF levels in specific brain regions, spinal cord and serum were determined by enzyme-linked immunosorbent assay (ELISA). Consistent with the results in PE patients, the concentration of serum BDNF decreased significantly from the sluggish rats to normal and rapid rats. Besides, in both brain regions and spinal cord, the sluggish group had the highest BDNF levels, while the rapid group had the lowest BDNF levels. Regression analyses of the expression of BDNF presented positive correlations between serum and brain (r = 0.958, p < .001), and between serum and spinal cord (r = 0.967, p < .001) respectively. Our findings suggested insufficient BDNF in the nervous system and serum may lead to rapid ejaculation. The current study adds to the evidence that BDNF is involved in the regulation of ejaculation.

Increased de novo glutathione production enhances sexual dysfunctions in rats subjected to paradoxical sleep deprivation

OBJECTIVE

Poor quality of sexual life has been reported secondary to poor sleep or sleep deprivation. Paradoxical sleep is an integral part of the sleep-wakefulness physiology and prolonged paradoxical sleep deprivation (PSD) may even be fatal. The objective of this investigation was to determine if D-ribose-L-cysteine (RibCys) and zinc (Zn) administration can attenuate the effect of PSD on the sexual function of male rats.

METHODS

Following acclimatization, 25 male rats were randomly distributed into five groups of 5 rats each. The PSD, PSD+RibCys, PSD+Zn, PSD+RibCys+Zn, and Control groups were sleep-deprived only, sleep-deprived and given 100mg/kg body-weight of pure RibCys, sleep-deprived and given 10mg/kg body weight Zn, sleep-deprived and given a combination of 100mg/kg of RibCys and 10mg/kg of Zn, and given distilled water without sleep deprivation, respectively. PSD lasted for 20 hours per day for 14 days. Subsequently, the sexual behavioral study was carried out and the animals were sacrificed for biochemical assays.

RESULTS

Analyses of results show that for animals treated with RibCys or Zn, all sexual parameters such as mount frequency and latency, intromission frequency and latency and ejaculation frequency and latency were significantly improved compared with animals subjected to PSD only. This improvement correlates strongly with serum glutathione (GHS) levels.

CONCLUSION

In summary, riboceine increases circulating GHS, which leads to improved sexual function during sleep deprivation.

Threshold for copulation-induced analgesia varies according to the ejaculatory endophenotypes in rats

Analgesia may be modulated by multiple internal and external factors. In prior studies, copulatory-induced analgesia was demonstrated using the vocalization threshold to tail shock (VTTS) in male and female rats. Three ejaculatory endophenotypes have been characterized in male Wistar rats based upon their ejaculation latency (EL). Since intromissions and ejaculations produce analgesia, and these copulatory patterns are performed with different frequency depending on the male's ejaculatory endophenotype, we hypothesized that copulation-induced analgesia would vary in relation to these endophenotypes. In the present study, we used three groups according to the EL (medians): rapid ejaculators (236 s; n = 21), intermediate ejaculators (663.2 s; n = 20) and sluggish ejaculators (1582.2 s; n = 8). Our aim was to evaluate whether copulation-induced analgesia is related to the ejaculatory endophenotypes during two consecutive ejaculatory series (EJS). In the first EJS, the VTTS of the rapid ejaculators was significantly higher than that of intermediate and sluggish rats. At the onset of the second EJS, the VTTS of the rapid and intermediate ejaculators was significantly higher than that of the sluggish rats. No differences in VTTS were observed during the first or second post-ejaculatory intervals among the three groups. These findings provide evidence that the more intromissions that occurred per unit time, the higher was the level of analgesia.

A Double-Blind, Placebo-Controlled Parallel Group Study to Evaluate the Effect of a Single Oral Dose of 5-HT1A Antagonist GSK958108 on Ejaculation Latency Time in Male Patients Suffering From Premature Ejaculation

BACKGROUND

Premature ejaculation (PE) is a common male neurobiological sexual disorder, related to a disturbance in central serotonin (5-hydroxytryptamine or 5-HT) neurotransmission.

AIM

To assess the efficacy of a single oral dose of 5HT_1A receptor antagonist GSK958108 on ejaculation latency time (ELT) in male subjects suffering from PE.

METHODS

A total of 35 male subjects were enrolled in a Phase 1 double-blind, placebo-controlled, parallel group masturbation-model study. All subjects completed the study. No subject was withdrawn from the study. There were no major protocol deviations reported during the study.

OUTCOMES

The primary outcome of the study was to evaluate the effect of a single oral dose of 5HT_1A receptor antagonist GSK958108 on ELT as measured in the masturbation model; additionally, we investigated drug's safety and tolerability.

RESULTS

In the 3 mg GSK958108 treatment group, the ELT was estimated to be 16% longer (1.542 vs 1.328, 95% CI: -16% to +61%) than if the subjects had taken placebo. In the 7 mg GSK958108 treatment group, the ELT was estimated to be 77% longer (2.346 vs 1.328, 95% CI: +28% to +144%) than in the placebo group. The systemic exposure to GSK958108 increased with dosage between 3 mg and 7 mg. A significant trend toward an increase of ELT was observed with increasing plasma concentrations of GSK958108. A total of 4 patients all treated with 7 mg dose experienced minor drug related adverse events (5 adverse events in 4 patients): somnolence (n = 3), headache (n = 1), tinnitus (n = 1).

CLINICAL IMPLICATIONS

In the current double-blind, placebo-controlled parallel group study the 5HT_1A receptor antagonist GSK958108 was tested in 3 mg and 7 mg doses for PE treatment in humans. It was shown that GSK958108 significantly delayed ejaculation showing a new and safe alternative in PE treatment.

STRENGTHS & LIMITATIONS

The present study showed innovative results suggesting an important role of 5HT_1A receptor antagonist in the PE treatment. However, the use of masturbation model and the small population are the main limitations of this investigation.

CONCLUSION

5HT_1A receptor antagonist GSK958108 3 mg per day and 7 mg per day was found to be well-tolerated, safe and effective for the treatment of PE subjects and demonstrated a strong association between 5HT1A receptors and ejaculation control in humans (NCT00861484). Migliorini F, Tafuri A, Bettica P, et al. A Double-Blind, Placebo-Controlled Parallel Group Study to Evaluate the Effect of a Single Oral Dose of 5-HT1A Antagonist GSK958108 on Ejaculation Latency Time in Male Patients Suffering From Premature Ejaculation. J Sex Med 2021;18:63-71.

Influence of Experimental Autoimmune Prostatitis on Sexual Function and the Anti-inflammatory Efficacy of Celecoxib in a Rat Model

Experimental autoimmune prostatitis (EAP) is a well-established model induced by an autoimmune response to prostate antigen. The symptomatic, pathological, and immunological characteristics of EAP animals are highly consistent with human chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS), which makes EAP an ideal model for this disease. Here, we investigate the influence of EAP on male rat sexual function and the efficacy of anti-inflammatory therapy with celecoxib. EAP rat models were established using male Wistar rats. Rats were randomly assigned to a normal control group, an EAP model group, or an EAP model with celecoxib treatment group (celecoxib group). Behavioral changes, sexual behavioral changes, and erectile function were estimated using an open-field test, a sucrose consumption test, mating experiments, and by intracavernous pressure/mean arterial pressure ratio (ICP/MAP). Histological changes in the prostate were observed by HE staining, and the serum inflammatory factors IL-1β and TNF-α levels were measured by enzyme-linked immunosorbent assay. In addition, serotonin (5-hydroxytryptamine, 5-HT), 5-HT_1A receptor, 5-HT_2C receptor, and serotonin transporter (SERT) expression levels in the hippocampus and spinal cord (T13–L1, L5–S2) were examined by immunohistochemistry and western blot analysis. Results showed that EAP rats exhibited characteristics of depression, decreased sexual drive, premature ejaculation, and increased threshold of penile erection. Moreover, all these changes were effectively alleviated by celecoxib. Significant increases in prostatic interstitial infiltration by inflammatory cells and in serum IL-1β and TNF-α levels were observed in EAP rats, and these were partially reduced by celecoxib. Additionally, the expression pattern of serotonin system regulators in the hippocampus and spinal cord were altered in EAP model rats, including a decrease in 5-HT levels and an increase in 5-HT_1A receptor levels. In conclusion, autoimmune prostatitis impaired rat sexual function, and this was effectively prevented by anti-inflammatory therapy with celecoxib. Moreover, a serotonin system disorder in the central nervous system was likely mediated via inflammation in EAP rats.

Premature ejaculation: an update on definition and pathophysiology

Premature ejaculation (PE) is the most common male sexual dysfunction, which represents a diagnostic as well as a therapeutic challenge for physicians. However, no universally accepted definition is currently available for PE. As a result, physicians continue to diagnose patients with PE according to major guidelines set by the professional societies. These guidelines either recommend the use of validated questionnaires or patient-reported outcomes. Recent efforts directed toward classifying PE may help provide a better understanding of the prevalence and risk factors of this disorder. While the exact etiology of PE has not been clearly elucidated, several risk factors have been strongly reported in the literature. Clearly, to understand the revised definition of PE, its etiology and pathophysiology is necessary to improve the clinical management of this medical condition and form the basis of future research in this regard. In this review, we highlight the past and current definitions of PE and present an appraisal on the classifications and theories suggested for the etiopathogenesis of PE.

Male Ejaculatory Endophenotypes: Revealing Internal Inconsistencies of the Concept in Heterosexual Copulating Rats

Distinct manifestations of sexual behavior are conceived as separate phenotypes. Each sexual phenotype is assumed to be associated with a characteristic brain. These notions have justified the phenotyping of heterosexual copulator males based upon their ejaculation's latencies (EL) or frequencies (i.e., cumulative ejaculation number; EN). For instance, men and male rats showing premature, normal or retarded ejaculation are assumed to be distinctive endophenotypes. This concept, nonetheless, contradicts past and recent evidence that supports that sexual behavior is highly variable within each sex, and that the brain sexual functional morphology represents an intricate sexual phenotypic mosaic. Hence, for ejaculatory male endophenotypes to be considered as a valid biological concept, it must show internal consistency at various levels of organization (including genetic architectures), after being challenged by intrinsic and/or extrinsic factors. We then judged the internal consistency of the presumed ejaculatory endophenotypes by assessing whether copulatory behavior and the expression of copulation relevant genes and brain limbic structures are specific to each of the presumed EL- or EN-ejaculatory endophenotypes. To do this, copulating male rats were first phenotyped in groups consistently displaying short, average or long ejaculation latencies or very high, high, average, low or very low EN, based in their copulatory performance. Then, the internal consistency of the presumed EL- or EN-endophenotypes was tested by introducing as covariates of phenotyping other copulatory parameters (e.g., number of intromissions) in addition to EL or EN, or by analyzing the expression levels of genes encoding for estrogen receptor alpha, progesterone receptor, androgen receptor, aromatase, DNA methyl-transferase 3a and DNA methyl-transferase 1 in the amygdala, medial preoptic area, ventromedial hypothalamus and olfactory bulb. We found that even though there were group-level differences in all the variables that were studied, these differences did not add-up to create the presumed EL- or EN-ejaculatory endophenotypes. In fact, the extensive overlapping of copulatory parameters and expression levels of copulation relevant genes in limbic structures across EL- or EN-phenotyped copulating male rats, is not consistent with the hypothesis that distinct ejaculatory endophenotypes exist and that they are associated with specific brain characteristics.

Pharmacological Studies on the Role of 5-HT1 A Receptors in Male Sexual Behavior of Wildtype and Serotonin Transporter Knockout Rats

Brain serotonin (5-HT) neurotransmission plays an important role in male sexual behavior and it is well established that activating 5-HT_{1 A} receptors in rats facilitate ejaculatory behavior. However, the relative contribution of 5-HT_{1 A} somatodendritic autoreceptors and heteroreceptors in this pro-sexual behavior is unclear. Moreover, it is unclear whether the contribution of somatodendritic 5-HT_{1 A} autoreceptors and postsynaptic 5-HT_{1 A} heteroreceptors alter when extracellular 5-HT levels are chronically increased. Serotonin transporter knockout (SERT^-/-) rats exhibit enhanced extracellular 5-HT levels and desensitized 5-HT_{1 A} receptors. These rats model neurochemical changes underlying chronic SSRI-induced sexual dysfunction. We want to determine the role of presynaptic versus postsynaptic 5-HT_{1 A} receptors in the pro-sexual effects of 5-HT_{1 A} receptor agonists in SERT^+/+ and in SERT^-/- rats. Therefore, acute effects of the biased 5-HT_{1 A} receptor agonists F-13714, a preferential 5-HT_{1 A} autoreceptor agonist, or F-15599, a preferential 5-HT_{1 A} heteroreceptor agonist, and S15535 a mixed 5-HT_{1 A} autoreceptor agonist/heteroreceptor antagonist, on male sexual behavior were assessed. A clear and stable genotype effect was found after training where SERT^+/+ performed sexual behavior at a higher level than SERT^-/- rats. Both F-15599 and F-13714 induced pro-sexual activity in SERT^+/+ and SERT^-/- animals. Compared to SERT^+/+, the F13714-dose-response curve in SERT^-/- rats was shifted to the right. SERT^+/+ and SERT^-/- rats responded similar to F15599. Within both SERT^+/+ and SERT^-/- rats the potency of F-13714 was much stronger compared to F-15599. S15535 had no effect on sexual behavior in either genotype. In SERT^+/+ and SERT^-/- rats that were selected on comparable low sexual activity (SERT^+/+ 3 or less ejaculations and SERT^-/- 5 or less ejaculations in 10 weeks) S15535 also did not influence sexual behavior. The two biased compounds with differential effects on 5-HT_{1 A} auto- and hetero-receptors, exerted pro-sexual activity in both SERT^+/+ and SERT^-/- rats. Applying these specific pharmacological tools has not solved whether pre- or post-synaptic 5-HT_{1 A} receptors are involved in pro-sexual activity. Moreover, the inactivity of S15535 in male sexual behavior in either genotype was unexpected. The question is whether the in vivo pharmacological profile of the different 5-HT_{1 A} receptor ligands used, is sufficient to differentiate pre- and/or post-synaptic 5-HT_{1 A} receptor contributions in male rat sexual behavior.

Learning and the Lifespan: What's Sex Got to Do With It?

Engagement in sexual behavior can impact neurosteroidogenesis, in particular production of the prohormone testosterone (T) and likely its subsequent metabolism to 5α-androstane-3α-17β-Diol (3α-Diol) or aromatization to estradiol (E2). Androgens and their metabolites vary across the lifespan and impact many behaviors, including cognition, anxiety, and sexual behavior. Thus, we hypothesized that mating may alter cognitive performance via androstane neurosteroids in an age- and experience-dependent manner. We first investigated if exposure to mating during memory consolidation could enhance performance in the novel object recognition task (NOR). Male rats were trained in NOR and then immediately exposed to mating-relevant or control stimuli. Following a 4 h inter-trial interval (ITI), male rats were tested for object memory. Male rats that were exposed to a receptive female during the ITI had better performance in NOR. We then investigated if these effects were due to novelty associated with mating. Male rats were exposed to mating-relevant stimuli and identified as sexually responsive (SR) or sexually non-responsive (SNR) based on a median split of engagement in mating with the stimulus female. We found that a brief history (10 min session daily for five consecutive days) of sexual history substantially influenced performance in the NOR task, such that SR males had better performance in the NOR task, but only when presented with the opportunity to mate during the ITI. As T levels substantially decrease with age in male rodents, we investigated whether the effects of long-term sexual experience (10 months) influenced neurosteroids and NOR performance in mid-aged (12 months old) males. Mid-aged SR males maintain neural T; however, they have decreased neural E2 and decreased cognitive performance at 12 months compared to mid-aged SNR rats. In sexually experienced rats, those with better cognitive performance had greater levels of T metabolites (e.g., 3α-Diol in mated SR males, E2 in mid-aged SNR rats). While naïve males that were mated during the ITI had better cognitive performance, T metabolites were decreased compared to controls. These findings suggest that T metabolites, but not the prohormone, may influence learning dependent on sexual proclivity, experience, and proximate opportunity to mate.

Tramadol's Inhibitory Effects on Sexual Behavior: Pharmacological Studies in Serotonin Transporter Knockout Rats

Tramadol is an effective pharmacological intervention in human premature ejaculation (PE). To investigate whether the inhibitory action of tramadol is primarily caused by its selective serotonin reuptake inhibitory (SSRI) effects we tested the dose–response effects of tramadol on sexual behavior in serotonin transporter wild type (SERT^+/+), heterozygous (SERT^+/-), and knockout (SERT^-/-) rats. To investigate whether other mechanisms contribute to the inhibitory effects, WAY100,635, a 5-HT_1A receptor antagonist and naloxone, a μ-opioid receptor antagonist, were tested on sexual behavior together with tramadol. Tramadol dose-dependently decreases sexual activity in all genotypes. In all studies, SERT^+/- rats did not respond differently from SERT^+/+ rats. WAY100,635 did not affect sexual activity in SERT^+/+, but dose-dependently reduced sexual activity in SERT^-/- rats. WAY100,635 (0.3 mg/kg) combined with tramadol (20 mg/kg) significantly reduced sexual activity in SERT^+/+ and even stronger in SERT^-/- rats. Naloxone did not affect sexual behavior consistently in SERT^+/+ rats, while in SERT^-/- rats all doses reduced ejaculation frequency mildly. Combining naloxone (20 mg/kg) and tramadol (20 mg/kg) decreased ejaculation frequencies in both genotypes. Interestingly, combining tramadol (20 mg/kg), WAY100,635 (0.3 mg/kg) and naloxone (20 mg/kg) led to complete elimination of all sexual activity in both SERT^+/+ and SERT^-/- rats. These findings suggest that the inhibitory effects of tramadol on male sexual behavior in SERT^+/+ rats is mainly, if not exclusively, due to SERT inhibition, with an important role for 5-HT_1A receptors, although influence of other systems (e.g., noradrenergic) cannot be excluded. As SSRIs exert their sexual inhibition after chronic administration, tramadol may be therapeutically attractive as “on demand” therapy for PE.

A Comparison of Sexual Side Effects of Antidepressants With and Without Naltrexone

OBJECTIVE

The aim of the study was to compare the rate of sexual side effects of the selective serotonin reuptake inhibitor paroxetine versus the tricyclic antidepressant desipramine and to examine the effect of co-prescription of naltrexone on sexual side effects among participants in a randomized clinical trial.

METHODS

This was a secondary analysis (N = 88) of veterans who participated in a 12-week trial. All veterans were randomized into one of four treatment groups: (a) desipramine/naltrexone, (b) desipramine/placebo, (c) paroxetine/naltrexone, and (d) paroxetine/placebo. The main outcome measure was the frequency of sexual side effects consisting of "decreased sex drive" and/or "impotence" reported by veterans at each weekly visit.

RESULTS

Approximately 61% of the veterans reported sexual side effects at least once during the trial, and 26.4% reported sexual side effects throughout the study. There were no significant differences in the frequency of sexual side effects among the four treatment groups. The results were similar when the comparison was made between the two antidepressant groups. There were no significant differences in the reporting of sexual side effects between those receiving desipramine and paroxetine. Also, the comparison between naltrexone and placebo did not alter the results.

CONCLUSIONS

This is the first study to compare frequency of sexual side effect reporting between paroxetine and desipramine. We found no statistically significant differences in sexual side effect reporting between the two antidepressants. Also, the addition of naltrexone did not show any beneficial effect on the sexual side effect profile.

Ejaculatory training lengthens the ejaculation latency and facilitates the functioning of the spinal generator for ejaculation of rats with rapid ejaculation

A spinal pattern generator controls the ejaculatory response. Central pattern generators (CPGs) may be entrained to improve the motor patterns under their control. In the present study we tested the hypothesis that training of the spinal generator for ejaculation (SGE) by daily copulation until ejaculation, could promote substantive changes in its functioning permitting a better SGE control of the genital motor pattern of ejaculation (GMPE) and, as a consequence, a normalization of the ejaculation latency of rats with rapid ejaculation. To that aim, we evaluated in sexually experienced male rats with rapid ejaculation (1) the effects of daily copulation to ejaculation, following different entrainment schedules, on their ejaculation latencies, (2) the impact of these different ejaculatory entrainment schedules upon the parameters of the GMPE and (3) the possible emergence of persistent changes in the functioning of the SGE associated to the daily ejaculation entrainment schedules. The data obtained show that intense ejaculatory training of rats with rapid ejaculation lengthens the ejaculation latency during copulation and augments the ejaculatory capacity of the SGE in this population when spinalized. Thus, present data reveal that like other CPGs, the SGE can be trained and put forward that training of the SGE by daily copulation to ejaculation might be a promising alternative that should be taken into consideration for the treatment of premature ejaculation.

Do rats have orgasms?

BACKGROUND

Although humans experience orgasms with a degree of statistical regularity, they remain among the most enigmatic of sexual responses; difficult to define and even more difficult to study empirically. The question of whether animals experience orgasms is hampered by similar lack of definition and the additional necessity of making inferences from behavioral responses.

METHOD

Here we define three behavioral criteria, based on dimensions of the subjective experience of human orgasms described by Mah and Binik, to infer orgasm-like responses (OLRs) in other species: 1) physiological criteria that include pelvic floor and anal muscle contractions that stimulate seminal emission and/or ejaculation in the male, or that stimulate uterine and cervical contractions in the female; 2) short-term behavioral changes that reflect immediate awareness of a pleasurable hedonic reward state during copulation; and 3) long-term behavioral changes that depend on the reward state induced by the OLR, including sexual satiety, the strengthening of patterns of sexual arousal and desire in subsequent copulations, and the generation of conditioned place and partner preferences for contextual and partner-related cues associated with the reward state. We then examine whether physiological and behavioral data from observations of male and female rats during copulation, and in sexually-conditioned place- and partner-preference paradigms, are consistent with these criteria.

RESULTS

Both male and female rats display behavioral patterns consistent with OLRs.

CONCLUSIONS

The ability to infer OLRs in rats offers new possibilities to study the phenomenon in neurobiological and molecular detail, and to provide both comparative and translational perspectives that would be useful for both basic and clinical research.

The pathophysiology of delayed ejaculation

Delayed ejaculation (DE) is probably least studied, and least understood of male sexual dysfunctions, with an estimated prevalence of 1–4% of the male population. Pathophysiology of DE is multifactorial and including psychosexual-behavioral and cultural factors, disruption of ejaculatory apparatus, central and peripheral neurotransmitters, hormonal or neurochemical ejaculatory control and psychosocial factors. Although knowledge of the physiology of the DE has increased in the last two decade, our understanding of the different pathophysiological process of the causes of DE remains limited. To provide a systematic update on the pathophysiology of DE. A systematic review of Medline and PubMed for relevant publications on ejaculatory dysfunction (EjD), DE, retarded ejaculation, inhibited ejaculation, and climax was performed. The search was limited to the articles published between the January 1960 and December 2015 in English. Of 178 articles, 105 were selected for this review. Only those publications relevant to the pathophysiology, epidemiology and prevalence of DE were included. The pathophysiology of DE involves cerebral sensory areas, motor centers, and several spinal nuclei that are tightly interconnected. The biogenic, psychogenic and other factors strongly affect the pathophysiology of DE. Despite the many publications on this disorder, there still is a paucity of publications dedicated to the subject.

The drug treatment of delayed ejaculation

Delayed ejaculation (DE) is an uncommon and a challenging disorder to treat. It is often quite concerning to patients and it can affect psychosocial well-being. Here we reviewed how DE is treated pharmacologically .We also highlighted specific settings where drugs could be introduced to medical practice. Electronic databases were searched from 1966 to February 2016, including PubMed MEDLINE, EMBASE, EBCSO Academic Search Complete, Cochrane Systematic Reviews Database, and Google Scholar using key words; delayed ejaculation, retarded ejaculation, inhibited ejaculation, drugs, treatment, or pharmacology. To achieve the maximum sensitivity of the search strategy and to identify all studies, we combined “delayed ejaculation” as Medical Subject Headings (MeSH) terms or keywords with each of “testosterone” or “cabergoline” or “bupropion” or “amantadine” or “cyproheptadine” or “midodrine” or “imipramine” or “ephedrine” or “pseudoephedrine” or “yohimbine” or “buspirone” or “oxytocin” or “bethanechol” as MeSH terms or keywords. There are a number of drugs to treat patients with DE including: testosterone, cabergoline, bupropion, amantadine, cyproheptadine, midodrine, imipramine, ephedrine, pseudoephedrine, yohimbine, buspirone, oxytocin, and bethanechol. Although there are many pharmacological treatment options, the evidence is still limited to small trials, case series or case reports. Review of literature showed that evidence level 1 (Double blind randomized clinical trial) studies were performed with testosterone, oxytocin, buspirone or bethanechol treatment. It is concluded that successful drug treatment of DE is still in its infancy. The clinicians need to be aware of the pathogenesis of DE and the pharmacological basis underlying the use of different drugs to extend better care for these patients. Various drugs are available to address such problem, however their evidence of efficacy is still limited and their choice needs to be individualized to each specific case.

Multiple Orgasms in Men-What We Know So Far

INTRODUCTION

There is much popular discussion on strategies to facilitate multiple orgasms in men (ie, 100,000+ hits in Google), yet the topic has not received an objective comprehensive review in the literature.

AIM

To review the literature on male multiple orgasms.

METHODS

We searched the literature for publications on "male multiple orgasms" and factors influencing male multiple orgasms in Google, PubMed, and PsychINFO. This yielded 15 relevant publications.

MAIN OUTCOME MEASURES

A comprehensive overview on the topic of male multiple orgasms and factors that influence the propensity of men to experience multiple orgasms.

RESULTS

Few men are multiorgasmic: <10% for those in their 20s, and <7% after the age of 30. The literature suggests 2 types of male multiple orgasms: "sporadic" multiorgasms, with interorgasmic intervals of several minutes, and "condensed" multiorgasms, with bursts of 2-4 orgasms within a few seconds to 2 minutes. Multiple orgasms appear physiologically similar to the single orgasm in mono-orgasmic men. However, in a single case study, a multiorgasmic man did not experience with his first orgasm the prolactin surge that usually occurs with orgasm in mono-orgasmic men. Various factors may facilitate multiple orgasms: (1) practicing to have an orgasm without ejaculation; (2) using psychostimulant drugs; (3) having multiple and/or novel sexual partners; or (4) using sex toys to enhance tactile stimulation. However, confirmatory physiological data on any of these factors are few. In some cases, the ability to experience multiple orgasms may increase after medical procedures that reduce ejaculation (eg, prostatectomy or castration), but what factor(s) influence this phenomenon is poorly investigated.

CONCLUSION

Despite popular interest, the topic of male multiple orgasms has received surprisingly little scientific assessment. The role of ejaculation and physiological change during the refractory period in inhibiting multiple orgasms has barely been investigated.

Psychiatric disorders and sexual dysfunction

Sexual problems are highly prevalent among patients with psychiatric disorders. They may be caused by the psychopathology of the psychiatric disorder but also by its pharmacotherapy. Both positive symptoms (e.g., psychosis, hallucinations) as well as negative symptoms (e.g., anhedonia) of schizophrenia may negatively interfere with interpersonal and sexual relationships. Atypical antipsychotics have fewer sexual side-effects than the classic antipsychotics. Mood disorders may affect libido, sexual arousal, orgasm, and erectile function. With the exception of bupropion, agomelatine, mirtazapine, vortioxetine, amineptine, and moclobemide, all antidepressants cause sexual side-effects. Selective serotonin reuptake inhibitors (SSRIs) may particularly delay ejaculation and female orgasm, but also can cause decreased libido and erectile difficulties. SSRI-induced sexual side-effects are dose-dependent and reversible. Very rarely, their sexual side-effects persist after SSRI discontinuation. This is often preceded by genital anesthesia. Some personality characteristics are a risk factor for sexual dysfunction. Also patients with eating disorders may suffer from sexual difficulties. So far, research into psychotropic-induced sexual side-effects suffers from substantial methodologic limitations. Patients tend not to talk with their clinician about their sexual life. Psychiatrists and other doctors need to take the initiative to talk about the patient's sexual life in order to become informed about potential medication-induced sexual difficulties.

Further definition on the multiple partner choice arena: a potential animal model for the study of premature ejaculation

INTRODUCTION

The multiple partner choice arena (MPCA) is an experimental setup in which male rats display a significant shortening of ejaculation latency, which is the main characteristic of premature ejaculation (PE) in men. Thus, the MPCA is a potential animal model for PE.

AIM

In this study, we further analyze whether the features of the MPCA satisfy the validity criteria for it to be considered an animal model as well as the possible participation of the serotoninergic system in the faster ejaculation exhibited by male rats in the MPCA.

METHODS

In Experiment 1, male rats were tested in a standard arena to assess their sexual behavior, then were assessed 1 week later in the MPCA. Another group was first tested in the MPCA, then in a standard arena. In Experiment 2, male rats divided into two groups were treated daily with WAY-100635 (5-HT(1A) antagonist) or vehicle for 15 days. In each group, half of the subjects were tested in a standard arena and half were tested in the MPCA on days 1, 8, and 15 of treatment.

MAIN OUTCOME MEASURES

Number of intromissions and intromission and ejaculation latencies were the main outcome measures.

RESULTS

In Experiment 1, males tested in the MPCA ejaculated significantly faster, regardless of the order in which they were evaluated in both arenas. In Experiment 2, the administration of WAY-100635 increased intromission and ejaculation latencies, and the number of intromissions in the MPCA.

CONCLUSIONS

The results obtained in the MPCA support its use as an animal model for PE evaluation.

Sexual side effects of serotonergic antidepressants: mediated by inhibition of serotonin on central dopamine release?

Antidepressant-induced sexual dysfunction adversely affects the quality of life of antidepressant users and reduces compliance with treatment. Animal models provide an instructive approach for examining potential sexual side effects of novel drugs. This review discusses the stability and reproducibility of our standardized test procedure that assesses the acute, subchronic and chronic effects of psychoactive compounds in a 30 minute mating test. In addition, we present an overview of the effects of several different (putative) antidepressants on male rat sexual behavior, as tested in our standardized test procedure. By comparing the effects of these mechanistically distinct antidepressants (paroxetine, venlafaxine, bupropion, buspirone, DOV 216,303 and S32006), this review discusses the putative mechanism underlying sexual side effects of antidepressants and their normalization. This review shows that sexual behavior is mainly inhibited by antidepressants that increase serotonin neurotransmission via blockade of serotonin transporters, while those that mainly increase the levels of dopamine and noradrenaline are devoid of sexual side effects. Those sexual disturbances cannot be normalized by simultaneously increasing noradrenaline neurotransmission, but are normalized by increasing both noradrenaline and dopamine neurotransmission. Therefore, it is hypothesized that the sexual side effects of selective serotonin reuptake inhibitors may be mediated by their inhibitory effects on dopamine signaling in sex brain circuits. Clinical development of novel antidepressants should therefore focus on compounds that simultaneously increase both serotonin and dopamine signaling.

Acoustic characterization of ultrasonic vocalizations by a nocturnal primate Tarsius syrichta

This preliminary study characterizes the ultrasonic vocalizations produced by Philippine tarsiers, Tarsius syrichta. Data were collected at the Philippine Tarsier Foundation Sanctuary in Corella, Bohol, Philippines, from July through October 2010. Recordings were made on a Wildlife Acoustics Ultrasonic Song Meter 2 BAT from 29 wild, free-living adult resident T. syrichta (23 females and six males). A total of 10,309 USVs were recorded. These vocalizations fell into three main categories: chirps, twitters, and whistles. Chirps were the most frequent, followed by twitters and whistles. Whereas chirps and twitters were emitted by both male and female Philippine tarsiers, whistles were only emitted by adult males. Given that vocalizations reported in this study were exclusively recorded during capture and handling, it is very likely that these vocalizations function as distress calls. However, as the long whistle was only given by adult males who were captured at the same time as the female or the group's infant, the function of the long whistle might be slightly different than the function of the other relatively lower-frequency USVs.

Pro-sexual effects of Turnera diffusa Wild (Turneraceae) in male rats involves the nitric oxide pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Turnera diffusa Wild has been used in folk medicine by its aphrodisiac and tranquilizing properties. Previously we experimentally showed the aphrodisiac effect of a chemically characterized aqueous extract of Turnera diffusa in male rats. However, the mechanism of action underlying such effects has not been studied.

STUDY AIMS

As part of our systematic studies of pharmacological properties of Turnera diffusa, we aimed to analyze whether the increased sexual motivation and the augmented sexual performance of sexually sluggish (SL) male rats treated with Turnera diffusa involves the NO pathway. Additionally we analyzed whether such effects were exerted at the level of the brain or the spinal cord. Finally, anxiety levels and ambulatory activity were also evaluated.

MATERIAL AND METHODS

Turnera diffusa (10-40 mg/kg) and sildenafil citrate (10 mg/kg) with or without a nonspecific inhibitor of NO synthase, Nω-nitro-L-arginine methyl esther (L-NAME, 12.5 mg/kg) were evaluated in SL rats, in a standard sexual behavior test and in the fictive ejaculation model in spinal cord transected and urethane-anaesthetized SL rats. Anxiety levels or ambulation were assessed in the burying behavior and open-field tests.

RESULTS

Turnera diffusa and sildenafil (both at 10 mg/kg) facilitated expression of male sexual behavior by shortening mainly ejaculation latency. Treatments also facilitated the number of discharges in the ejaculatory motor pattern as well as the number of ejaculatory motor patterns and its associated penile erections. L-NAME prevented the pro-sexual effects of treatments on both experimental models. Besides, the extract of Turnera diffusa (10 mg/kg) produced an anxiolytic-like effect in male rats without affecting ambulation.

CONCLUSIONS

Findings from the present work support the notion that pro-sexual effect of the aqueous extract of Turnera diffusa in rats involves the participation of NO pathway, mainly at central level. The anxiolytic-like effect of Turnera diffusa is an advantage to its use for improving sexual performance.

Therapeutic targets for premature ejaculation

Premature ejaculation (PE) is the most common male sexual complaint, and may exert a profound negative impact on the man's life and partnership. Using currently available treatment alternatives (e.g., selective serotonin uptake inhibitor, agents acting locally on the penis), PE can be treated in most, but not all patients. However, since long term success rates have been disappointing, and the only approved treatment so far is the short-acting selective serotonin re-uptake inhibitor dapoxetine, there is currently an intensive search for new treatment modalities. Selection of the most promising therapeutic targets from a host of current and potential candidates depends heavily on their roles in the pathophysiology of PE. Possible central nervous targets that will be discussed are serotonin transporters, and CNS receptors for 5-HT(IA) and 5-HT(1B), dopamine, oxytocin, opioids, neurokinin-1, and glutamate. Putative peripheral targets include α(1)-adrenoceptors, phosphodiestrase enzymes, Rho kinases, purinergic (P2X) receptors, and penile sensory nerves. It is clear that exploiting the full therapeutic potential of these targets will require additional basic and clinical research.

Current therapeutic strategies for premature ejaculation and future perspectives

Premature ejaculation (PE) is a common sexual disorder in men that is mediated by disturbances in the peripheral and central nervous systems. Although all pharmaceutical treatments for PE are currently used 'off-label', some novel oral agents and some newer methods of drug administration now provide important relief to PE patients. However, the aetiology of this condition has still not been unified, primarily because of the lack of a standard animal model for basic research and the absence of a widely accepted definition and assessment tool for evidence-based clinical studies in patients with PE. In this review, we focus on the current therapeutic strategies and future treatment perspectives for PE.

Future sexual medicine physiological treatment targets

INTRODUCTION

Sexual function in men and women incorporates physiologic processes and regulation of the central and peripheral nervous systems, the vascular system, and the endocrine system. There is need for state-of-the-art information as there is an evolving research understanding of the underlying molecular biological factors and mechanisms governing sexual physiologic functions.

AIM

To develop an evidence-based, state-of-the-art consensus report on the current knowledge of the major cellular and molecular targets of biologic systems responsible for sexual physiologic function.

METHODS

State-of-the-art knowledge representing the opinions of seven experts from four countries was developed in a consensus process over a 2-year period.

MAIN OUTCOME MEASURES

Expert opinion was based on the grading of evidence-based medical literature, widespread internal committee discussion, public presentation, and debate.

RESULTS

Scientific investigation in this field is needed to increase knowledge and foster development of the future line of treatments for all forms of biological-based sexual dysfunction. This article addresses the current knowledge of the major cellular and molecular targets of biological systems responsible for sexual physiologic function. Future treatment targets include growth factor therapy, gene therapy, stem and cell-based therapies, and regenerative medicine.

CONCLUSIONS

Scientific discovery is critically important for developing new and increasingly effective treatments in sexual medicine. Broad physiologic directions should be vigorously explored and considered for future management of sexual disorders.

Toward evidence-based genetic research on lifelong premature ejaculation: a critical evaluation of methodology

Recently, four premature ejaculation (PE) subtypes have been distinguished on the basis of the duration of the intravaginal ejaculation latency time (IELT). These four PE subtypes have different etiologies and pathogeneses. Genetic research on PE should consider the existence of these PE subtypes and the accurate measurement of the IELT with a stopwatch. Currently, three methods of genetic research on PE have been used. They differ in the investigated population, tool of measurement, study design, and variables of PE. From animal and human research, it is derived that the central serotonergic system "modulates" ejaculation, whereas the ejaculation (reflex) itself is probably not under direct influence of the serotonergic system, but rather under the influence of other neurotransmitter systems in the spinal cord. For genetic research on PE, it is important to take into account that the (serotonergic) modulation of the IELT is variable among men and may even be absent. This means that serotonergic genetic polymorphisms may only be found in men with PE who respond with an ejaculation delay treatment with a selective serotonin reuptake inhibitor.

Dapoxetine: in premature ejaculation

Dapoxetine, a selective serotonin reuptake inhibitor, is the first oral pharmacological agent indicated for the treatment of men aged 18-64 years with premature ejaculation. In four randomized, double-blind, placebo-controlled, multicentre studies of 12-24 weeks' duration, oral dapoxetine 30 or 60 mg (administered as needed) was effective in the treatment of men with premature ejaculation, inducing significantly (p < 0.001) greater improvements from baseline than placebo in the primary efficacy endpoint (mean intravaginal ejaculatory latency time [IELT] or mean average IELT [defined as the average of IELT values over the previous 4 weeks], as measured by the female partner utilizing a stopwatch). For the most part, dapoxetine recipients achieved significantly better outcomes than placebo recipients with regard to the secondary endpoints, including the Premature Ejaculation Profile (PEP) domains and the Clinical Global Impression or Patient Global Impression ratings of change in premature ejaculation, across these clinical studies. The beneficial effects of dapoxetine therapy on the perceived control over ejaculation and satisfaction with sexual intercourse PEP domains were sustained in a 9-month noncomparative extension phase of two identical 12-week, double-blind studies. Oral dapoxetine therapy for up to 12 months was generally well tolerated in men with premature ejaculation, with the nature of treatment-emergent adverse events generally similar across the clinical studies and between dapoxetine and placebo.

Drug-induced sexual dysfunction in rats

This unit describes the testing of sexual behaviors of male Wistar rats. The described test enables the detection of stimulatory and inhibitory profiles of compounds. The test includes four training sessions to reach a stable sexual performance, followed by acute and/or chronic administration of drugs. The main quantifiable sexual behaviors are number of mounts (no vaginal penetration), intromissions (vaginal penetration), and ejaculations. By comparing the test compound to reference compound(s), sexual (side) effects can be determined.

Postmating change in physiology of male Drosophila mediated by serotonin (5-HT)

Sex peptides transferred during mating from male to female fly profoundly influence the female's behavior and physiology, including an increase in the movement of eggs along the oviduct. In the male ejaculatory duct, the authors have identified peristaltic waves that travel distally with an average frequency of 0.6 Hz. The frequency of peristalsis is increased by 0.1 microM serotonin (5-HT) and completely blocked by 5-HT antagonists (IC(50)< 1 microM). The authors also report that mating affects the male reproductive tract; peristaltic waves along the ejaculatory duct are significantly reduced postcopulation by 30%. Serotonergic neurons innervate the ejaculatory duct, but their genetic ablation does not prevent peristalsis. The authors propose that peristalsis may be modulated by serotonin circulating in the hemolymph. As serotonin is linked with attentiveness in both flies and mammals, this bioassay suggests reduced behavioral sensitivity of the male fly after mating.

Oxytocin-messages via the cerebrospinal fluid: behavioral effects; a review

The cerebrospinal fluid (CSF) usually is considered as a protective 'nutrient and waste control' system for the brain. Recent findings suggest, however, that the composition of CSF is actively controlled and may play an influential role in the changes in brain activity, underlying different behavioral states. In the present review, we present an overview of available data concerning the release of oxytocin into the CSF, the location of the oxytocin-receptive brain areas and the behavioral effects of intracerebroventricular oxytocin. About 80% of the oxytocin-receptive areas are located close to the ventricular or subarachnoid CSF, including the hypothalamic 'Behavior Control Column' (L.W.Swanson, 2003). As a conclusion we suggest that 'CSF-oxytocin' contributes considerably to the non-synaptic communication processes involved in hypothalamic-, brainstem- and olfactory brain areas and behavioral states and that the flowing CSF is used as a 'broadcasting system' to send coordinated messages to a wide variety of nearby and distant brain areas.

Pharmacogenetics and pharmacogenomics of sexual dysfunction: current status, gaps and potential applications

Although treatment of different types of sexual dysfunction has improved in the past decade with the introduction of phosphodiesterase type 5 inhibitors and selective serotonin reuptake inhibitors, response rates to these targeted therapies are variable. There are a number of studies in the published literature that provide proof-of-concept that genetic variation contributes to the variable response. Pharmacogenomics will most likely be one part of our therapeutic armamentarium in the future and will provide a stronger scientific basis for optimizing drug therapy on the basis of each patient’s genetic constitution. This article will review English language medical literature on the state-of-the-art genetic polymorphisms of drug targets, transporters and signaling molecules as well as pharmacogenetic studies of sexual dysfunction and suggested possible applications. Collectively, the data demonstrate that pharmacogenomics in the field of sexual medicine is still in its infancy. More research will provide further intriguing new discoveries in years to come.